Highly active antiretroviral treatment (HAART) of HIV infection is associated with dramatic fall in the amount of HIV in the blood. The effects on the immune system are positive but less dramatic. Restoration of the immune system is now a goal of chronic HIV therapy. Interleukin-2 is a substance which is naturally produced by the body's CD4 cells. People with HIV-1 infection do not produce enough IL-2. IL-2 has been shown to increase CD4 cells in HIV-1 patients by 2-4fold. Trials with intravenous IL-2 produced much toxicity in theform of "flu" symptoms.